The objective of the research is to determine the functional organization of descending cerebral cortical and midbrain tegmental influences on somatic sensory transmission in the vertebrate spinal cord. Combined electrophysiological and neuroanatomical studies in can and monkey are used to identify and characterize what types of spinal sensory neurons are influenced by the descending systems and what afferent inputs exist to the cells of origin of the descending pathways exerting spinal sensory control.